1. Field of the Invention
The present invention generally relates to hard disk drives (HDDs), and more particularly, the present invention relates to bias compensation for servo control of HDDs.
A claim of priority is made to Korean Patent Application No. 10-2005-0082440, filed on Sep. 5, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Description of the Related Art
A hard disk drive (HDD) is an auxiliary storage unit of a computer system which is capable of accessing bulk data at high speed by magnetically reading/writing data from/on a rotating magnetic disk. That is, data is stored in concentric tracks formed on the magnetic disk, and the tracks are accessed by a magnetic head for writing or reading data on or from the magnetic disk. The operation of moving the magnetic head across the magnetic disk and positioning the head above one of the tracks is referred to as a “track seek” operation.
In the track seek operation, various disturbances affecting the magnetic head is referred to as a “bias”. Bias forces affecting the magnetic head may include, for example, atmospheric pressure against a side surface of the head resulting from air flow generated when the disk is rotating, stresses caused by a flexible cable connected to the head, and bearing axis characteristics of a voice coil motor (VCM).
It is also known that the bias varies with a position, a moving distance, and a moving direction of the magnetic head. Therefore, for example, since an initial driving force of a voice coil varies with the position and moving direction of the magnetic head in a track seek operation, and since an initial moving speed of the magnetic head varies with the moving distance, the bias is compensated for according to the position, moving distance, and moving direction of the magnetic head. Methods of compensating for the bias are disclosed in Korean Registered Patent Nos. 403,037 and 260,411 and U.S. Pat. Nos. 5,773,948 and 6,738,220.
According to a conventional bias compensation method, a disk is divided into a plurality of zones from the inner circumference to the outer circumference, a bias is measured in each zone and stored in a bias table, and the bias is compensated for by referring to the bias table when a track seek is performed.
Since bias can vary with the operational environment, it is preferable that all biases corresponding to all zones of the disk in the bias table be updated with changes in operational environment. However, the calculations needed to update the bias table in this manner are complex and require long computation times.